Late Weichselian varve archives re-explored to assess proglacial sedimentary chronologies using the principles of tree-ring analysis

Abstract

Glaciogenic varves are formed annually in proglacial basins and provide detailed geochronological archives about the dynamics of deglaciation. Varve chronologies are constructed from multiple varve series measured at individual localities. Temporal connection between the series is traditionally achieved by visual comparison of varve-thickness variations. This connection method resembles that of dendrochronological cross-dating. By contrast, dendrochronological correlation proceeds through the routine of statistical (along with visual) comparisons between the tree-ring series, providing quantification of the dating results, their veracity and robustness. Here we demonstrate the advantages and convenience of applying tree-ring statistical methods to varve records, using an extensive varve archive originating from southern Finland. The data series of individual varve-thickness diagrams were metamorphosed by detrending, prewhitening and averaging, that is, by the methods adopted from tree-ring science. Subsequently, it was seen that the series having 80 or more varves have a higher potential to be unambiguously cross-dated than shorter series. The varve-thickness diagrams could be categorized into two types, those having regional chronological importance and those showing only subregional (distance < 20 km) correlativity. The varves of former type ought to be regarded as primary constituents of the geochronology. The varves of latter type have low geochronological validity although they may bear local sedimentological importance. The findings have the potential to modernize the science of varve-based geochronologies.